Provided is a base adjustment device and method of a polyphase filter that can reduce an area and power consumption, and operate at a high speed. The band adjustment device of the polyphase filter according to the present invention includes a voltage-controlled oscillator (VCO), a polyphase filter that inputs an output from the VCO, a mixer that receives an output from the polyphase filter, an envelope detection circuit (envelope detector) that inputs an output from the mixer, and a band control signal generation circuit that inputs an output from the envelope detector.